Radio beacon system



June 1, 1943. KEAR 2,320,521

RADIO BEACON SYSTEM Filed Feb. 27, 1935 2 Sheets-Sheet 1 F17. .2 F27. EE 7.3

I Fiy- 5 F 7f 5 I. 5 1a [3102:]

AMPLIFIER g E Qwue/wbom [E5 FRANK G. KEAR v '9 AMPLIFIER 3 E $53 June1., 1943.

F. G. KEAR RADIOBEACON SYSTEM Filed Feb. '27-, 1935 2 Sheets-Sheet 2FRANK G. KEAR Patentecl June 1, 1943 RADIO BEACON SYSTEIE Frank G. Kear,Washington, D. C., assigncr to Washington Institute of Technology,

Inc.,

Washington, D. (3., a corporation of Delaware Application February 2'7,1935, Serial No. 8,541

20 Claims.

This invention relates to radio beacon systems and, more particularly,to the establishing of a two-course or four-course beacon system by theuse of non-directional radiators.

It has heretofore been proposed to substitute for the crossed looptransmitting means, as originally employed in radio beacon transmission,a system employing four vertical antennas, such change being proposed inorder to do away with the errors introduced into the radio beaconoperation by the inherent nature of the crossed loop system. It has beenfound, however, that the systems employing four vertical antennas arenot entirely free from certain disadvantages inherent in the crossedloop systems. In the use of a beacon system employing either the crossedloop or four-vertical antenna types of array, the characteristic signalis reversed on opposite sides of the beacon transmitter. Thus, in avisual system, it is necessary to turn the reed box over as thetransmitter is passed, in order to maintain the previous relation of thecharacteristic signals. In an aural system the pilot, when passing thebeacon transmitter, must constantly remember the reversed arrangement ofsignals in order to correctly orient the aircraft with respect to thetransmitter. It may also be noted that the use of the four verticalantennas has materially increased the installation cost of the system.Further, in the use of a system employing four vertical antennas as atransmitting array, it is necessary to maintain the tuning of thevertical antennas and the phasing of the currents in them in order tomaintain the stability of the courses, it being necessary in suchsystems to correctly tune and phase four circuits.

It is therefore an object of the present invention to providetransmitting means for providing a two-course or four-course beacon,which means will not be subject to the errors and disadvantages of priorsystems.

A primary object of the invention is to provide a transmitting systemfor providing either a twocourse or four-course beacon, which systemwill employ, in either case, only two non-directional radiators.

Another object of the invention is to provide a transmitting system forproviding either a twocourse or four-course beacon, which system willnot be subject to errors resulting from reflection from theKennelly-Heaviside layer.

Another object is to provide a transmitting system for a two-coursebeacon in which system the same characteristic signal will always befound on the same side of the beacon course, thereby further aiding insimplifying the navigation of aircraft.

A further object is to provide a transmitting antenna array which willrequire less tuning and phase adjustment than prior systems in order tomaintain course stability.

A further object is to provide circuit arrangements and means forenergizing two non-directional radiators to provide either a two-courseor four-course beacon.

Other objects and novel features of the invention will be made apparentto those skilled in the art by the following description and the annexeddrawings which, it will be understood, are merely illustrative of theinvention and impose no limitation thereon not imposed by the appendedclaims.

Referring to the drawings, in which similar reference numerals refer tolike parts,

Fig. 1 illustrates the field pattern resulting from the energization ofthe antennas of a two-antenna system in one manner,

Fig. 2 illustrates the field pattern resulting from the energization ofthe antennas of a two-antenna system in a second manner,

Fig, 3 illustrates the combined field pattern resulting from the.combination of the field patterns of Figs. 1 and 2, according to thepresent invention,

Fig. 4 is a schematic drawing of an antenna arrangement for producingthe field patterns of Figs. 1, 2 and. 3,

Fig. 5 discloses a circuit arrangement for the antennas in accordancewith the schematic showing of Fig. 4,

Fig. 6 discloses a circuit arrangement for energizing the circuit ofFig. 5,

Fig. 7 discloses a second circuit for energizing the circuit of Fig. 5,

Fig. 8 illustrates the field pattern resulting from the energization oftwo non-directional radiators in a system for the production of afour-course beacon,

Fig. 9 illustrates the field pattern resulting from the energization, ina different manner, of two non-directional radiators, for the productionof a four-course beacon,

Fig. 10 illustrates the combination of the field patterns of Figs. 8 and9,

Fig. 11 is a schematic view showing the arrangement of twonon-directional radiators for transmission of a four-course beacon,

Fig. 12 is a schematic showing of a system for energizing the antennasof Fig. 11,

Fig. 13 is a circuit diagram illustrating a secnd circuit arrangementfor transmitting a twocourse beacon from two non-directional radiators,and

Fig. 14 is a circuit diagram illustrating a second circuit arrangementfor transmitting a fourcourse beacon from two non-directional radiators.

It has been determined that if two non-directional radiators be sospaced and the currents in the antennas so phased that the algebraic sumof the space and time phase angles is 180, a space pattern of cardioidform will be produced, the maximum of which will extend alon a linejoining the two antennas and in the direction of the lagging antenna.This effect is illustrated in Fig. 1, it being noted that in thisexample the antennas are spaced one-quarter wave length or 90 and theenergization of antenna Vv' leads that of antenna E by 90. If a currentbe supplied to the antennas so that the energization of antenna W lagsthat of antenna E by 90, a cardioid extending in the opposite directionwill be produced. This effect is illustratedin Fig. 2 and it will benoted that in this case the maximum of the cardioid pattern is on theline joining the two antennas and in the direction of antenna W. If,now, the antennas be energized either alternately or simultaneouslytwo-coursebeacon are separated 90 in space and are energized by currentsdisplaced 90 in time phase. It is tobe understood that these values areonly a special case of the invention and are employed only for thepurpose of simplifying the discussion. It is contemplated by theinvention that the two non-directional radiators be spaced K degreesapart and energized by currents displaced R degrees in time phase, whenK+Rl80.

In Fig. 4 there is schematically illustrated a radiating array accordingto the present invention which is so arranged as to establish radiationfields providing two courses in space.

This arrangement comprises the antennas E, W which will be assumed to bespaced a quarter Wavelength apart. These antennas may be supplied withmodulated radio frequency energy through transmission lines 3, 4 and,according to the present invention, are connected by a transmis sionline I which in this example has an electrical length of 90. It will beapparent that voltage supplied to radiator E will produce a similarvoltage in radiator W with a 90 time lag, while a voltage supplied toradiator W will produce a similar voltage in radiator ,E with a 90 timelag.

A circuit arrangement for the antenna system illustrated in Fig. 4 isdisclosed in Fig. 5 and it will be seen that in this circuit arrangementradio frequency voltages modulated by differing characteristic signalsare applied at C, D from a radio frequency source (not shown) to thetransmission lines 3, 4 through coupling transformers 5, 6. Eachof thetransmission lines 3, 4

includes the primary I of a transformer, each of said transformershaving two secondaries 8, 9. The secondary 8 of each transformer isconnected in a circuit l9 comprising a transmission line having anelectrical length of 90, While the secondaries 9 are respectivelyconnected to nondirectional radiators E, W which are grounded at it andM, respectively. It will be noted that the antennas E, W are spaced aquarter wavelength apart in accordance with the schematic showing ofFig. 4, although as stated above, the invention contemplates that theantennas be spaced K degrees apart and energized by currents displaced Rdegrees in time phase, when K+R l80.

It will be seen that if a voltage is supplied to antenna E through thetransmission line 3, primary 1 and secondary 9, a similar voltage willbe supplied to the transmission line I9 through primary l and secondary8 and a similar voltage with a 90 time lag will, therefore, be producedin antenna 'W. A cardioid field pattern will be produced by suchenergization and such pattern will have its maximum in a line joiningthe antennas E, W and extending in the direction of antennaW. Similarly,energy supplied directly to antenna W through transmission line 4,primary l and secondary 9 'will be transmitted to antenna E throughtransmission line! and will appear there with a lag equal to the lengthof line H]. A second cardioid-shaped field will be produced by theradiation'of this energy, the maximum of such field being in the line E,W and in the direction of antenna E. If equal power is supplied toantennas E or W either simultaneously or alternately, reverse-phasecardioids will be produced in the manner described and theirintersection will lie on a line erpendicularly bisecting a line joiningthe two antennas, such line of intersection providing a course extendingin two directions from the antenna station.

The radio frequency energy supplied to the two antennas may be modulatedwith any desired signals in order to define the course. The usual A andN signals for aural beacons or the 87 and 65 cycle signals for visualbeacons may be employed. In the operation of a system employingcharacteristic signals of this type, one of the two cardioids will beproduced from the radio frequency energy modulated by the A or 87 cyclesignal, while the other cardioid will be produced from the radiofrequency energy modulated by the N or 65 cycle signal. It will,therefore, be seen that each of the two cardioids will be impressed withonly one of thetwo characteristic signals. Each signal 'will'thereforealways be greater than the otheron one side of the course defined bytheline of intersection of the radiating fields of the antennas and anaircraft flying along such course will not encounter any reversal ofindication.

As stated above, the desired space patterns may be produced alternatelyif a so-called aural beacon is to. be provided at a receiver located inthe radiated fields, or continuously if a so'-c'alled visual beacon isdesired. A circuit for supplying voltages alternately to the circuitsC,D of Fig. 5 is disclosed in Fig. 6. In this circuit a master oscillatorl5 supplies voltages at radio frequency to a beacon amplifier l5, theoutput of which is connected to a link circuit l'l containing a keyingrelay it which may be operated to alternatelyenergize th circuits 0 andD to supply power to lines 3 and 4. When line 3 is'excited the arraywill produce a cardioid whose carrier at the keying relay l8.

If a visual system is being employed, the circuit for energizing theantennas of Fig. may

be as disclosed in Fig. 7. In this circuit a master oscillator l9supplies voltages at radio frequency to the two amplifier branches 20,2|, these branches being coupled respectively to the circuits 0 and Dfor supplying the lines 3 and 4. Any desired coding, such as the 87 and65 cycle audio frequency modulations, may be impressed on the carriersand supplied continuously to the antennas E and W. It will therefore beseen that the array will constantly produce two cardioids, one havingits maximum in the direction of one antenna and being modulated with the87 cycle frequency, and the other having its maximum in the direction ofthe other antenna and being modulated with th 65 cycle frequency. Theline of intersection of the two cardioids will perpendicularly bisectthe line joining the two antennas and it will be seen that th 8'1 cyclefrequency and the 65 cycle frequency will each always be of greatestintensity on one side of the course on both sides of the line joiningthe antennas. Consequently, it will not be necessary for the pilot of anaircraft flying on the course to turn over the reed box or, if a reedconverter is used, switch over the converter when crossing over thebeacon station. The course may be bent as desired by varying therelative amplitudes of the voltages supplied to the lines. The beaconsidebands, being of different frequency, will not combine in space butwill produce a pair of cardioid patterns, as described, with a course inthe same line as in the case of the aural beacon. The carriers willcombine in space but the resultant carrier from each antenna is in timephase with the other and the pattern is an ellipse of slighteccentricity which will not disturb th courses.

The invention also provides other means for providing a two-coursebeacon by the radiation of energy from two non-directional radiators insuch a manner as to establish two intersecting radiated fields each ofwhich will have a cardioid transmission characteristic and which will bereversed in phase. By this means according to the invention, there isprovided a circuit for supplying to two non-directional radiatorsvoltages -which would cause the establishment of a radiated field havinga circle pattern, a circuit for supplying to the non-directionalradiators currents which would cause the establishment of a radiatedfield having a figure-of-eight pattern, and a circuit for combiningthese currents and supplying such combined currents to thenondirectional radiators. The combined currents will caus the radiationfrom the antennas of energy so phased as to produce two reversed phaseradiation fields each of which will have a cardioid transmissioncharacteristic. The intersections of these radiated fields will definetwo courses in space extending on opposite sides of the line joining thetwo antennas. Such means are disclosed in Fig. 13 of the drawings.

The system disclosed in Fig. 13 comprises a bridg circuit L having thearms 40, 4|, 42 and 43, which arms are connected at terminals 44, 45, 46and 41. Fixed condensers 48 and 49 are inserted in arms 40 and 4|. Twonon-directional radiators E and W are provided and are coupled to groundthrough inductance coils 50, 5| which form the secondaries of inputtransformers, the primaries 52 and 53 of which are included in thecircuit of a transmission line 54 having an electrical length of in thepresent case. The antennas E and W are spaced, in the case underdiscussion, a quarter wave-length apart. The transmission line 54 alsoincludes a coil 55, the same being in inductive relation to-a primarycoil 56, the purpose of which arrangement will appear more fullyhereinafter. Voltages at radio frequencies and modulated to provide anycharacteristic signals desired are supplied through input circuits C, Dto input transformer 51, 58. One terminal of the secondary of inputtransformer 51 is connected by lead 59 to terminal 45 of the bridge L,while the other terminal of the said output transformer is connected toterminal 41 of the bridge through lead 60. The output terminals of thetransformer 58 are connected to bridge terminals 44 and 46 through leadsBI and 62 respectively. Th circuit across terminals 45, 46 of the bridgeis completed by leads 65, 66 which are connected at their one ends tothe terminals 45, 46 and at their other ends to the terminals of primarycoil 56. The circuit across terminals 46 and 41 of the bridge iscompleted by leads 61, 68, one of which, lead 51, is connected at itsone end to bridge terminal 45 and at its other end to the midpoint 69 oftransmission line 54, which point is also connected to ground at 10. Theother lead 68 is connected at its one end to bridge terminal 41 and atits other end to the secondary coil 55 in the transmission line 54 by acenter-tap 1|.

Assuming that voltages at radio frequency and modulated by any desiredcharacteristic signals are being supplied to input circuits C and D,current will flow from the secondary of transformer 51 through lead 59to bridge terminal 45 where it divides, part flowing through arms 4| and40 of the bridge and lead (ill to the other terminal of transformer 51.The rest of thecurrent flows through bridge arm 42, lead 56, winding 56,lead 65, bridge arm 42, bridge arm 43, lead 61, terminal 69,transmission line 54, windings 52 and 53, winding 55, center-tap 1| ofwinding 55, lead 68, bridge arm 43 and lead 60 to the secondary oftransformer 51, thereby completing the circuit. It will be seen, first,that the completion of this circuit energizes winding 56 causing acurrent to flow therein. Current in winding 56 will induce a current inwinding 55, whch, being series connected to the windings 52, 53 willcause currents to flow in opposite directions in these coils. Thevoltages across coils 52, 53 will thus be displaced in phase. Suchexcitation of windings 52, 53 will induce voltages having a phasedisplacement of 180 across antenna coils 50, 5| and a radiated fieldhaving a figure-ofeight form will be produced.

The above-described circuit being completed between terminal 69 andcenter-tap 1|, in-phase voltages will be impressed across windings 52,53, these windings being connected in parallel with the terminal 69 andcenter-tap 1|. Such excitation of windings 52 and 53 will cause in-phasecurrents to be induced in the antenna coils 50, 5| and a radiated fieldhaving substantially a circle form will be produced.

The in-phase and reversed-phase voltages across antenna coils 50, 5|will not-causeseparate fields to be produced, but the combined currentsin the antenna coils willproduce a radiated field of cardioid shape,resulting -from the combination of the circle and figure-of-eight field.In the case under discussion, the leads 65,

66 compose a transmission line or time delay circuit whose total delayis of the order of an odd multiple of ninety degrees, plus or minus.

Current from circuit D will flow through lead 62 to bridge terminal 46where it divides, establishing two circuits. One of these is completedthrough bridge arm 42, lead 65, coil '56, lead 66, bridge arms 42and..4l and lead 6! to the second terminal'of the input circuit. Theother circuit is completed through bridge arm 43, lead 61, terminal 69,transmission line 54, windings 52 and 53, winding 55, center-tap H, lead68, bridge arms 43 and 40 and lead 6| to the second terminal of theinput circuit D. It is evident, from the principles of Wheatstone bridgecircuits, that the result of this flow of current is to produce acrossthe arm 42 the sum of the two voltages at a given instant, and across,arm 43'the difference of these voltages, or vice-versa. This effect isindependent of the phase relation of the ,volt- 5 ages applied at C andD, although for convenience this is customarily 90. It is understoodthat should carrier suppressed transmission be employed this phase anglehas reference to the angles between the axes of projection of the side.-band frequencies considered as rotating. vectors. The voltages acrosswindings 52 and .5.3j'.will be 180 displaced in phase due to theseriesconnectionof the elements and. reversed-phase voltages will thereforeibeinduced in lantenna coils 50, 5| thereby producing a radiated .field: offigure-of-eight form.

The terminal 69. and center-tap .H being connected in parallel acrosswindings 52, 53, voltagesapplied across these two points will causein-phase currents to fiow in windings, '52, 53 which will inducein-phase currents in antenna coils 50, 5|. A radiated field havingcircleform will therefore be produced. As discussed above, the circle andfigure-of-eight .fields will combine in space to produce a cardioidfield whosemaximum will lieon a linejoining thetwo antennas andextending ina direction opposite. to thatof the cardioid, field producedby currents from,input circuit C. This action is caused by theoperationof the bridge circuit as previously described.

It will therefore be seen that two radiatedfields of cardioid shapeandhaving. their maximums extending in opposite directions .willbeproduced. These fields may be produced alternately in the case of anaural system'by alternate energization of input. circuits C and D, ormay be simultaneously produced by continuous .energization oflthe .two.circuits, if .a visualsystem isdesired. In:.either case the carrierssupplied to thetwo course for aerial navigation.

The-present-invention also contemplates the provisionoi means .forproducing a-four-course beacon froina system employing onlyv twonondirectional radiators. As stated hereinbefore. it has heretofore beenproposed to provide a fourcourse beacon by energizingfour verticalantennas in pairs to produce two intersecting fig,- ure-of-eight patterns,the points ofintersection of which determine four courses inspace. 7Such systems have been substituted for the prior crossed p systems inorder to eliminate the effects due to reflection from the Kennelly-Heavisidelayer, known as night efiects. By reason of the presentinvention it is possible to produce a four-course beacon by the use ofonly two non-directional radiators, thereby materially reducing theinstallation costs of the transmitting system, and eliminating errorsdue to night effeet.-

It may be desirable to establish a four-course beacono-f either theaural or visual type and while the followingdiscussionspecificallyrelates to a visual system, it will be applicableto an aural system as well. The visual system employs usually the 87cycle and-65 cycle modulations of the carrier to provide characteristicsignals. According to the present invention two non-directionalradiators E-and W, as disclosed in Fig. 8, are provided and are spaced ahalf wave-length apart. These antennas are supplied with voltages atradio frequency modulated by the 87 cycle frequency. If the 87 cycleantenna currents are in time phase a figure-of-eight field asillustrated in Fig. 8 results. The same antennas aresupplied withvoltages at radio frequency modulated by the 65 cycle frequency. Ifthe-65 cycle antenna currents are separated in time phase,.-thefigure-of-eight field of Fig. 9 results. If the two antennasbe excitedsimultaneously oralternately in this manner, the two figure-of-eightfields combine as illustrated in Fig. 10, the overlapping portionsthereof providing four equi-signal courses OP, 0Q, OR and OS. Theangular relation of the four courses may be varied by varying relativelythe amplitudes of the supplied V0ltages.

A schematic showing of an antenna. array for the production ofthefieldsdescribed is illustrated in Fig. 11. The antennas E, W are.spaced a half wave-length apart and are separately excited throughtransmission lines X and Y. Anexciting circuit for the antennas E and Wis illustrated in Fig. 12 and it will be seen that this circuit providesfor the supplying of both the 65 cycleand 87 cycle frequencies to bothofthe antennas. A source of radio frequency (not shown) may supplyvoltages atradio frequency to modulating circuits for impressing thesignal frequencies. The output of the modulating circuit 30 is suppliedthrough leads 32 to the line X which supplies antenna E, and throughleads 33 to the line Y which supplies antenna W, these voltages being inphase. The output of modulating circuit 3! is suppliedto line X throughleads 34 and in out-of-phase relation to line Ythrough leads 35.Voltages having an identifying characteristic, such as the 65 cyclemodulation for example, are supplied to the two antennas in in-timephasefrom the modulating circuit 30 and produces a figure-of-eight field ofthe type illustrated in Fig; 8, due. to the phasing of the currents andthe spacing of the antennas. The 87 cycle currents supplied to one ofthe antennas from the modulating circuit 3| are 180 out of time phasewith the currents of the same frequency supplied to the other of theantennas, thereby producing a figure-of-eight field of the typeillustrated in Fig. 9. Simultaneous energization of the two antennas bythe 87 cycle and 65 cycle frequencies, in the manner described, willproduce a combined field resulting from the combination of the in-phaseand out-of-phase frequencies, which field will be of the doublefigureof-eight type as illustrated in Fig. 10. The two figure-of-eightfields overlap in space and the points of intersection of the fieldsdetermine four courses for aerial navigation.

It will be apparent that if an aural system is desired the lines may beenergized by alternate in-phase and out-of-phase voltages modulated bythe usual A and N or other desired signals. The spacing of the antennas,and the phasing of the exciting currents will remain the same and thefield produced will also be the same, except that at any given instantonly one of the fields of Figs. 8 and 9 will exist.

A second means according to the invention for producing a four-coursebeacon from a circuit employing two non-directional radiators isdisclosed in Fig. 14. In this circuit there is provided an antenna arrayconsisting of the two nondirectional radiators E and W which are spacedhalf a wave-length apart and are connected by transmission lines SI, 89at the junction of which are connected two coils 82, 84 of athree-winding transformer, the terminals of coil 84 being conmodulatedby any desired characteristic signal.

A second source of radio frequency current modulated by any desiredcharacteristic signal is connected by leads 9|, 92 to coils 82 and 84through center-taps.

If radio frequency currents modulated by any desired characteristicsignal, such as the usual A or N signal for an aural system or the 87cycle and 65 cycle signals for a visual system, are sup plied to coils82 and 84 through leads 9|, 92 which are connected to the centers ofsuch coils, inphase voltages will be supplied to antennas E and W and aradiated field of figure-of-eight form having its major axis at an angleof 90 to the line joining the antennas will be produced. If carrierfrequency currents modulated by any desired characteristic signal arenow supplied to coil 83 through leads 85, 86, similar voltages will beinduced in coil 82 and 84 and out-of-phase voltages will be supplied toantennas E and W, whereby a radiated field of figure-of-eight form willbe produced, and such field will have its major axis on the line joiningthe antennas. The two fields so produced will combine in space toproduce a field of the type shown in Fig. 10 and the intersections ofthe fields will provide four courses in space for aerial navigation.

The foregoing description and the annexed drawings disclose certainforms of the invention, but it will be apparent to those skilled in theart that modifications and improvements of the invention may be madewithout departing in any way from the spirit or scope of the invention,for the limits of which reference must be had to the appended claims.

I claim:

1. A radio beacon system comprising two spaced non-directional antennas,means connect ing said antennas and having a known electrical length,two sources of difierently modulated radio frequency current forexciting said antennas, and means for dividing the current from eachsource to supply to said antennas from each source in-phase andout-of-phase currents.

2. A radio beacon system comprising two spaced non-directional antennas,a transmission line connecting said antennas, means for inducing seriescurrents in said transmission line to produce out-of-phase currents insaid antennas, and means for inducing parallel currents in saidtransmission line for producing in-phase currents in said antennas,whereby a radiated space pattern resulting from the combination of saidin-phase and out-of-phase antenna currents is produced.

3. In the production of a radio beacon through the agency of a pair ofspaced radiators connected to the opposite sides of a phase-shiftingnetwork, the steps of amplitude modulating a carrier with two differentaudio frequency signals to thereby produce two separate waves eachresulting from a difierent one of such modulations; continuouslysupplying one of said waves to one of said sides of said network andcontinuously supplying the other of said waves to the other of saidsides of said network; and radiating the resultant waves from saidradiators.

4. In a radio beacon, the combination which comprises: a phase-shiftingnetwork having first and second sides; means for continuously supplyinga wave resulting from amplitude modulation of a carrier of givenfrequency with one modulation frequency to the first side of saidnetwork; means for continuously supplying a wave resulting fromamplitude modulation of a carrier of the same given frequency withanother modulation frequency to the second side of said network; and apair of spaced radiators respectively connected to the first and secondsides of said network.

5, A radio beacon system comprising two spaced non-directional antennas,an exciting circuit inductively coupled to one of said antennas forenergizing said antennas with one of a pair of signals, a secondexciting circuit inductively coupled to the other of said antennas forenergizing said antennas with the other of said pair of signals, and atransmission line having a predetermined electrical length inductivelycoupled to both said exciting circuits.

6. In a radio beacon, the combination of a source of radio frequency,means for modulating a portion of the radio frequency produced by saidsource at an audio frequency, phasing means and antenna radiating meansfor radiating in a definite direction said modulated radio frequencywith a space pattern cardiodal in shape, additional means for modulatinga portion of said radio frequency at a second audio frequency differentfrom said first audio frequency, a second phasing means associated withsaid second modulated radio frequency and producing a second spacepattern in space cardioidal in shape from said radiating means and in adirection opposite to said first pattern, said first and said secondcardioidal space patterns intersecting in space to form two zones wheresaid first modulated radio frequency is equal in intensity to saidsecond modulated radio-frequency.

'7. A radio beacon system for establishing a plurality of zones of equalsignal intensity comprising two spaced non-directional antennas, meansfor producing in said antennas voltages causing a radiation having acardioid field pattern whose major'axis is inthe direction of one of theantennas, andmeans for simultaneously producing in said antennasvoltages causing a radiation having a cardioid field pattern whosemajoraxis is in the direction of the other of said antennas, andmeansfor differently modulating the energy in said antennas in order toproduce differently modulated cardioid radiation fields:

8. A radiobeacon system' for establishing a plurality of zones'of equalsignal intensity comprising two spaced non-directional antennas, meansfor periodically producing in said antennas voltages causing a radiationhaving a cardioid-fieldpattern whose major axis is in the direction ofone of the antennas, and means operating alternately with said firstmeans for producing in said antennasvoltages causing a radiationhaving acardioidfield pattern whose major axis is in thedirectionof theotherofsaid antennas, and means for differently modulating the energyin'saidantennas in order to produce difierently modulated cardioid radia- 0tion fields.

9. 'A radio beacon system'comprising two nondirectional antennas spacedK degrees apart, a transmission line having an electrical length of Rdegrees connecting said antennas, two sources of-modu1ated-radiofrequency energy supplying said antennas; a bridge circuit connected tosaid sourcesand to said transmissionline for di viding the currents fromsaidsources and supplying aplurality of--in-phase and a plurality ofout-of-phase currents to= said transmission line whereby twointersecting field patterns are radiated fromsaid antennas, and K+R-=180.

10, A radio beacon'systenr for producingtwo intersecting cardioid-shapedradiated fields, comprising two non-directional radiators spaced K'apart, means for-supplying directly to one of saidradlators radiofrequency energy characterized by one-of .two different signals, meansfor supplying directly to the other of said radiators radio frequencyenergy characterized by the second of said signals, and means having anelectrical 1 length of R connecting said radiators whereby modulatedenergy directly supplied to each radiator will appear in the other witha phase displacement of R, the sumof K and R being approximately 180;

11. A radio beacon system according to'claim' 10, in which atransmission line having an electricallength of- R connects thetworadiators.

121A method of producing a-radio beacon with a pairof spaced radiatorsconnected to the opposite sides of a phase-shiftingnetwork, whichincludes the steps of continuously supplying to one of said sides ofsaid phase-shifting network a wave resulting from amplitude modulationof a carrier of given frequency with a modulation frequency,continuously supplying to the other of said'sides of said phase-shiftingnetwork a wave resulting from amplitude modulation of a carrier ofsaidgiven frequency with a difierent modulation frequency, wherebyduringsome instants of-time one of said waves has a greater amplitude at saidphase-shifting network than the in which other of said waves and duringother instants of time the said one wave has less amplitude at saidphase-shifting network than said other wave,

thereby causing the resultant waves received at said radiators to havedifferent phase relations at difierent instants of time, and radiatingthe resultant waves received at said radiators.

13. In the production of a radio beacon through the agency of a pair ofspaced radiators connected to the opposite sides of a phase shiftingnetwork, the steps of continuously supplying a wave resulting fromamplitude modulation of a carrier of given frequency with one audiofrequency signal to one of said sides of said network, continuouslysupplying a wave resulting from amplitude modulation of a carrier ofsaid given frequency with another audio frequency signal to the other ofsaid sides of said network, whereby during some instants of time one ofsaid network than. theother and during other instants of time said onewave has a greater am.- plitude at said phase-shifting network than saidother wave, thereby causing the resultant waves relations at differentinstants of time, and radiating .the resultant waves received at saidradiators.

14. In a radio beacon, the combination which comprises a phase-shiftingnetwork having first and second sides, a source of carrierwavesconnected to said first and second sidesof said network, meanscontinuously connected .between.

said source and said first side ofsaid network for modulating saidvcarrier with an audio frequency signal, means continuously connectedbetween said source andsaid second side of said network for modulatingsaid carrier with a diftennas, and means for simultaneously produc-.

ing in said antennas voltages having a figure-ofeight field patternwhose major axis is in a line at right angles to the line joining theantennas.

16. An equi-signal radio beacon system com? prising two non-directionalantennas spaced apart by a distance approximately equal to .one-.

half of the radiated wavelength, means for. ex-.

exciting said antennas in 180 outeof-phase relation with the other ofsaid, signals to thereby produce two figure-of-eight shaped fields.each.

60 of which is respectively characterized byone of said signals andwhich overlap inspace to provide zones within which said signals are ofequal intensity. 17. An equi-signal radio beacon-system comprising twonon-directional antennas spaced apart by a distance approximately equalto onehalf of the radiated wavelength, means for exciting said antennasin in-phase relation with one of a pair of diiferent signals andmeansfor simultaneously exciting said antennas in 180 out-of-phaserelation with the other of said signals to thereby simultaneouslyproduce two figure-of-eight shaped fields each of which is 75characterized by one of said signals which overwaves has less amplitudeat said phase-shifting received at said radiators to have difierentphase.

citing said antennas in in-phase relation with. one of a pair ofdifferent signals and means for lap in space to provide zones withinwhich said signals are of equal intensity.

18. An equi-signal radio beacon system comprising two spacednon-directional antennas, a transmission line having inductive couplingto both of said antennas, a three winding transformer two of the coilsof which are respectively connected in opposite branches of saidtransmission line, means connecting the mid-points of said coils to asource of radio frequency energy on which is impressed one of a pair ofdifferent signals whereby energy characterized by such signal issupplied in in-phase relation to said antennas, means connecting theends of the third coil of the transformer to a source of radio frequencyenergy on which is impressed the second of said signals whereby energycharacterized by said second signal is supplied in 180 out-ofphaserelation to said antennas, whereby there are produced twofigure-of-eight shaped fields each of which is characterized by one ofsaid signals and which overlap in space to provide zones within whichsaid signals are of equal intensity.

19. An equi-signal radio beacon according to claim 18, in which energyis alternately supplied to the first-named two coils of the transformerand then to the third coil thereof.

20. An equi-signal radio beacon according to claim 18, in which energyis simultaneously supplied to the first-named two coils of thetransformer and to the third coil thereof.

FRANK G. KEAR.

